1. Field of the Invention
The present invention relates generally to an impulse signal detection apparatus and a wireless ranging method using the impulse signal detection apparatus, and, more particularly, to an impulse signal detection apparatus and method which enables a wireless real-time location system application in an indoor/outdoor multipath fading environment by using an ultra-short impulse signal.
2. Description of the Related Art
In general, wireless real-time location technology enables the location (tracking) of humans, animals and objects, the management of patients in a hospital, and the management of expensive equipment to be performed in real time, so that systems have been implemented using a variety of types of methods such as ZigBee, and a Wireless Local Area Network (WLAN).
However, since it is very difficult to achieve as a good precision as tens of centimeters in an environment of multipath fading, interest in the development of wireless real-time location technology using an impulse radio ultra wideband signal, which is a new wireless method, is growing.
Impulse radio ultra wideband (IR-UWB) wireless technology is designed to use an impulse waveform. With regard to this, U.S. Federal Communications Commission (FCC) permitted the use of a frequency band for ultra-wideband wireless technology in February 2002, and in Europe, Japan and Korea, frequency bands for related technology are allocated.
Meanwhile, an impulse signal has a signal bandwidth equal to or wider than hundreds of MHz in the frequency domain, and has a pulse width equal to or narrower than a nano second (10−9 sec), which is much narrower than the repetitive period of a pulse, in the time domain. Accordingly, an impulse signal has excellent temporal precision characteristics and, therefore, may be used for precise ranging. In particular, in August 2007, the IEEE 802.15.4A standardization group announced a de facto international standard for short distance data communication technology having an impulse signal-based low-speed, low-power, low-complexity wireless location function, and many efforts to develop related technologies have been made throughout the world. Furthermore, the International Organization for Standardization (ISO)/International Electrotechnical Commission (IEC), which are international standard organizations, are establishing standards for impulse signal ultra-wideband technology-based real-time location system (RTLS).
Conventional technologies corresponding to the impulse signal ultra-wideband technology-based real-time location technology will be described below.
U.S. Pat. No. 5,510,800 (entitled “Time-of-Flight Radio Location System”) issued to the Regents of the University of California on Apr. 23, 1996 discloses a system capable of measuring a very accurate location by detecting the location of a first arriving pulse by applying an RF impulse to a structure in which transmission and reception are separated from each other. That is, the system uses a method of capturing a first arranging pulse using a peak detector. However, in the case of a multipath fading environment, impulses are gathered together and then input due to a multipath, and the selection of an accurate threshold level is difficult because the size of the closest line-of-sight is much less than the magnitude of overlapping of multipath fading signals. That is, it is impossible to use the first pulse detection method using a peak detector.
U.S. Pat. No. 6,882,315 (entitled “Object Location System and Method”) issued to Mutispectral Solutions, Inc. on Apr. 19, 2005 discloses a location system using an impulse UWB signal. That is, a method in which a reference transmitter is added in a multipath fading environment and the synchronization between transmitters and a direct path in a multipath fading environment are found is disclosed. However, there is no description of a method of finding a pulse. In particular, there is no description of a method of directly finding a pulse in a multipath fading environment.
U.S. Pat. No. 6,133,876 (entitled “System and Method for Position Determination by Impulse Radio”) issued to Time Domain Corporation proposes an idea for precisely measuring distance using an impulse signal. That is, distance is measured using the difference in impulse propagation time between a transmitter and a receiver. In order to perform reception, a correlator is used. However, this ranging method has the disadvantage of requiring an existing mixer and the disadvantage of needing to know the accurate timing and the information of a received pulse.
The paper “Ranging in a Dense Multipath Environment using a UWB Radio Link” published on December 2002 in the IEEE Journal on selected areas in communications, VOl. 20, No. 9 by Joon-Yong Lee and Robert A. Scholtz proposes an algorithm for detecting a rectilinear path signal. Although a mixer and a high-speed sampler are used to implement the above structure, this increases the complexity and cost of the system.
Furthermore, the paper “Experimental Investigation of an IR-UWB Positioning System with Comparators” published on November 2007 in the IEICE Trans. Fundamentals Vol. E90-A, No. 11 by Koichi KITAMURA and Yukitoshi SANADA proposes a structure in which a high-speed comparator is used to detect an impulse signal. The proposed structure digitizes received impulses in a multipath fading environment using a high-speed comparator, and symbols are detected from the digitized signal by a signal processing unit using a correlator. However, this proposed structure has an advantage in that in a multipath fading environment, the interval of a received pulse is long, so that ranging errors may be increased.
Furthermore, the paper “A Low-complexity Noncoherent IR-UWB Transceiver Architecture with TOA Estimation” published on April 2006 in the IEEE Trans. on Microwave Theory and Techniques, VOL. 54, No. 4 by Lucian Stoica and Alberto Rabbachin and Ian Oppermann discloses a scheme for finding the greatest output by integrating a received impulse signal with respect to a single transmission pulse using an integrator having a parallel structure. However, there are disadvantages in that a plurality of integrators is required to implement the above method and power consumption is increased by these integrators.
As described above, although the impulse signal wireless technology provides very excellent resolution, a low-complexity, low-cost technology for detecting the precise timing of an impulse signal in a multipath fading environment has not been proposed.